This song is in a language called Lingala. It is sung as a lullaby, or by canoe paddlers to pace the paddle strokes. (source)

Translation

Olele! Olele! The current is very strong
Row! Row! His country, His country is the Kasai*.
Olele! Olele! The current is very strong.
Eh eho, eh eh eheho, let Benguela** come!
Come! Come! The courageous one.
Come! Come! The generous one.
Come! Come!
Olele! Olele! The current is very strong

*Uele and Kasai are rivers in Congo.
**Benguala is a cold current in the waters off the south west coast of Africa that brings winds with it.
(source)